1. Field of the Invention
The present invention relates to a drive circuit for driving an ink jet head installed on an ink jet printer, the ink jet head having a plurality of head parts in each of which piezoelectric elements are arranged corresponding to plural nozzle openings and ink droplets are ejected from the nozzle openings by applying a drive signal produced when charging and discharging of a condenser connected to the piezoelectric elements. In particular, the present invention relates to a drive circuit with a regulation circuit which is in common with each of the head parts, thereby a voltage waveform of the drive signal in each head part can be totally regulated by the regulation circuit, therefore it can easily realize multi-head part construction (multi-nozzle construction) in the ink jet head.
2. Description of Related Art
Conventionally, in an ink jet head of piezoelectric type in which piezoelectric elements are used as ink ejection means, a drive signal (drive voltage), which abruptly changes, is applied to the piezoelectric element arranged on a nozzle opening, thereby volume change occurs in the piezoelectric element and volume of an ink room filled with ink changes. Thus, various printings are conducted on a recording medium by ejecting ink droplets from the nozzle openings.
Here, the piezoelectric element is equivalent to a condenser (capacitance) taking into its electric characteristic, thus, if a voltage waveform of the drive signal applied to the piezoelectric element is made simply rectangular waveform, an input current to the piezoelectric element becomes large, as a result, there is a problem that the drive circuit will be broken. Taking the above circumstances into consideration, as the voltage waveform of the drive voltage to drive the piezoelectric element of the ink jet head, a trapezoid waveform or a triangle waveform of the drive voltage is used in the conventional ink jet head so as to make the input current to the piezoelectric element small. In case of that the voltage waveform of the drive voltage is made a trapezoid waveform or a triangle waveform, it is well-known that a gradient of the drive voltage affects an ink ejecting velocity and an ink ejecting quantity in the ink jet head, therefore it is necessary to control the gradient of the drive voltage.
In order to satisfy the above demand, it is used in the drive circuit of the ink jet head in the arts a regulation circuit to regulate a current value in a condenser (capacitance) and a constant-current circuit. Through the constant-current circuit, electric charge is charged in and discharged from the condenser, and the voltage waveform obtained by controlling the gradient of the drive voltage based on the current value of the constant-current circuit is produced. Further, after the voltage waveform is amplified by an amplifier the piezoelectric element is driven by the amplified voltage waveform.
However, in the above drive circuit of the ink jet head, if a plurality of head parts are installed in the ink jet head corresponding to color printing (in this case, a plurality of head parts are installed according to ink colors used for color printing and a plurality of nozzle openings and piezoelectric elements are formed in each head part), current flowing into the amplifier from the circuit producing the voltage waveform of the drive signal increases. Thereby, the voltage waveform changes differently from each other in a case that ink is ejected from the one head part and in another case that ink is ejected from the plural head parts.
To avoid the above cases, the condenser (capacitance), the constant-current circuit, the regulation circuit for regulating current in the constant-current circuit and the amplifier are constructed in one drive circuit unit. In this case, it is necessary to construct a plurality of drive circuit units in accordance to number of the head parts, and further it is necessary to regulate the voltage waveform of the drive signal every each drive circuit unit.
In case that it is necessary to stagger drive timing of the nozzle with a voluntary time every head part at the time of drive control of each head part, a plurality of drive circuit units should be inevitably used and the voltage waveform of the drive signal should be regulated every each drive circuit unit.